ABC News just confirms that a Chinese national has contacted the National Broadcaster, claiming responsibility for the hacking incident. This is the relevant section from the news report:

The hacker has contacted the ABC saying he does not work for the Chinese Government and is just an ordinary, angry Chinese citizen who objects to the film.

The film’s director Jeff Daniels says he is concerned about the fact Victoria police will be putting on extra security for the screening.

“I personally find it appalling that the Chinese Government has put the film festival and film-goers in a position where they need a police escort and private security to see a film,” he said.

“I think Melbourne is getting a small taste of the position that the Chinese Government has put Rabiya Kadeer and her family and the Uighur population in for the past 60 years.”

The film festival organiser reiterates that the Kadeer film will be screened as schedule.

This author once again urges Chinese authorities and their representatives in Australia to cooperate with the Australian Police in tracking down the hacker(s) responsible for this act of cyber-terrorism.

“We will uphold whatever the enemies oppose, while we oppose whatever the enemies uphold”.(凡是敌人反对的，我们就要拥护；凡是敌人拥护的，我们就要反对）。——节选自《和中央社、扫荡报、新民报三记者的谈话》（一九三九年九月十六日），《毛泽东选集》第二卷第五八零页。

In obedience to your great instruction, we should uphold Rebiya and Dalai Lama, due to that the CCP has been reduced to the public enemy of the whole human being, therefore what the enemy CCP opposes will surely be supported, right?